How to Planetary Treasure, Basically
From PSP2i Wiki
Why is the Planetary Treasure such a pain, eh?
Why are we getting Planetary Treasures?
Because we need Extend Code, Fusion Codes, and Extend Code Infinitys. Also because CalorieMate Maple are very OP.
Planetary Treasures By Grade
First off, two things:
one, we will ignore obtaining of specific Mission Discs during this guide. Check Mission Discs to find where the specific ones are, or Downloadable content if you are using that, as it contains every Boss, Area, Enemy Table and Block count.
two, after obtaining the appropriate mission, obtaining the Planetary Treasure is simply a matter of "running it till you get it", and there's nothing interesting there (nothing to improve the drop rates, either).